Interfacial evolution in Cr/Mo-coated Zr alloys near the Mo-Zr eutectoid temperature

This study investigates the interfacial evolution of Cr/Mo-coated Zr alloys near the Mo-Zr eutectoid temperature, from the viewpoints of microstructure and chemical composition and with the joint application of XRD, TEM and EDS analyses. The experimental findings highlight significant changes in microstructure and diffusion behavior associated with the Mo-Zr eutectoid reaction. In the as-fabricated specimen, it is noted that introducing a Mo-intermediate layer results in the formation of an amorphous Cr layer at the Cr/Mo interface. In the case of the annealing temperature below the Mo-Zr eutectoid reaction, Mo interlayer effectively impedes the diffusion between Cr and Zr, thereby suppressing the formation of intermetallic compounds. However, the diffusion barrier function of Mo interlayer deteriorates when the temperature exceeds the eutectoid point, with the presence of four distinct diffusion zones, including α-Zr, β-Zr, the intermetallic compound Zr(Mo,Cr,Fe)₂, and the Mo layer containing fine Zr(Mo,Cr,Fe)₂ particles. These findings underscore the critical role of Mo-interlayer in influencing the structural stability and intermetallic compound formation in Cr/Mo-coated Zr alloys, not only at the temperature regime around the eutectic reaction, but also at the temperature regime around the eutectoid reaction, which is of great necessity for the practical applications of accident tolerant fuel cladding under high temperature environment.